Laser machining systems and methods are commonly used to machine various types of materials and structures. Such laser machining systems and methods may provide a number of advantages including lower manufacturing costs, increased throughput and production yield, and improved quality. In the area of solar panels, for example, the advantages of laser machining could significantly enhance the efficiency and viability of solar energy technology.
In the manufacture of thin film photovoltaic (PV) solar panels, laser machining techniques may be used to scribe the various thin film layers in a panel to form electrically connected cells. In one type of PV solar panel, three layers are deposited to form the panel and lines are scribed after each new deposition. The area on the panel including these lines is considered a wasted area that does not contribute to solar energy conversion. Thus, the lines should be straight and aligned accurately to minimize this wasted area and to provide the best efficiency. High scribing speeds and increased throughput are also desirable. Providing accurate high speed scribing of thin film PV solar panels (and other similar structures) presents a number of unique challenges.
Scribing lines on a workpiece with a laser beam involves moving the workpiece and/or the laser beam linearly. For large area workpieces, moving the workpiece at high speeds to effect scribing may be difficult or impossible, and it is often desirable to move the laser beam across the workpiece. Moving a laser beam delivery system, however, may adversely affect the positional accuracy and uniformity of the laser beam on the workpiece. Moreover, splitting a laser beam into multiple beamlets for scribing a workpiece may result in undesirable scribe variations such as variations in width, depth, fluence, heat-affected-zones and penetration, which can adversely affect the precision of the scribes.
Another challenge with laser machining of PV solar panels is the ability to maintain accuracy with the long working distance from the laser source to the workpiece and the large size of the panels. Angular pointing instability may result from the long working distance and longer beam delivery path. When the laser beam must travel longer distances to the workpiece and far-field scribing techniques are used, for example, the position of the laser spot focused on the workpiece can vary due to laser pointing variations, resulting in inaccuracies in line straightness and alignment.
The choice of the laser also presents challenges because of the nature of the thin film layers being scribed and because of the desire to lower the manufacturing cost of solar panels. Existing laser machining systems and methods often use single mode coherent beams. Using a coherent beam spot, however, may not result in the desired selective material removal and may not efficiently use the beam power.